A known type of fluid-tight connector means for connecting together opposite ends of two pipes, or tubes, comprises flanges provided on the ends of the pipes to be joined. A fluid-tight seal between the tubes may be obtained by bolting the flanges together around the circumference of the pipes. It is difficult and time consuming, however, to provide a circumferentially uniform seal with such an arrangement and, in order to improve the uniformity, it is common to insert an annular elastomeric gasket between the opposed flanges. It is often undesirable, however, to use elastomeric gaskets in hostile environments, such as those involving high temperatures, high pressures, or corrosive fluids in which they are likely to quickly decompose. In such hostile environments it is necessary to rely only upon metal-to-metal seals and to accept the above mentioned disadvantages.